1. Field of the Invention
The object of the invention are enzyme immobilizates prepared by building a hydrophobic matrix based on silica by sol-gel processing in the presence of lipases, the process of preparing same, and application thereof.
2. Description of Related Art
Employing lipases in technical applications meets with increasing interest in hydrolysis or synthesis of esters as well as in transesterification reactions under moderate conditions, inter alia, where hydrophobic substrates are predominantly employed (K. D. Mukherjee, Biocatalysis 1990, 3, 277-293; T. Nielsen, Fette, Seifen, Anstrichmittel 1985, 87, 15-19). Due to their substrate specificity often being broad, lipases are used not only in lipids chemistry but more and more frequently also for stereoselective reactions in organic synthesis. Lipases have also found application in therapeutics. They are used for treatment of digestive insufficiencies caused by pancreatic diseases or cystic fibrosis. An important factor for the economic efficiency of an enzymatic process is a suitable method for the immobilization of the biocatalyst in order to allow ready recovery and multiple use of the enzyme as well as to achieve, if possible, an increase of its stability under the reaction conditions. The prior art in this field of enzyme technology has been summarized several times in review literature, e.g. for lipases (F. X. Malcata, H. R. Reyes, H. S. Garcia, C. G. Hill, Jr., and C. H. Amundson in J. Am. Oil Chem. Soc. 1990, 67, 890-910). In some instances, immobilization by incorporating the lipase in a solid matrix results in an improved activity yield and stability, as compared with other methods, but in most cases is more complicated to perform. Preparation of SiO.sub.2 gels by sol-gel processing (C. J. Brinker, G. W. Scherer, Sol-Gel-Science: The Physics and Chemistry of Sol-Gel-Processing, Academic Press, San Diego 1990; L. L. Hench, J. K. West, Chem. Rev. 1990, 90, 33-72) through hydrolysis of tetraalkoxysilanes, such as tetramethoxysilane or tetraethoxysilane, can be used to incorporate biomolecules in the inorganic matrix. For the immobilization of lipases, however, this method is not suitable since it provides only very unsatisfactory activity yields.